1. Field of the Invention
The present invention relates to an optical disk on which information (e.g., digital video information) can be stored at a high density.
2. Description of the Related Art
In recent years, the recording density of optical disk media goes on increasing. On an optical disk medium on which data or information can be written by a user, a track groove has normally been formed in advance and a recording film has been formed so as to cover the track groove. Data or information is written by the user on the recording film along the track groove, i.e., either on the track groove or on an area (land) interposed between adjacent parts of the track groove.
The track groove is formed so as to wobble just like a sine wave and a clock signal is generated in accordance with a wobble period. Synchronously with this clock signal, user data is written on, or read out from, the recording film.
To write data at a predetermined location on an optical disk, address information (or location information), indicating physical locations on the optical disk, needs to be allocated to, and recorded at, respective sites on the optical disk while the disk is being manufactured. Normally, an address is allocated to a series of areas that are arranged along a track groove and have a predetermined length. There are various methods for recording such address information on an optical disk. Hereinafter, a conventional method for recording an address on an optical disk will be described.
Japanese Laid-Open Publication No. 6-309672 discloses a disk storage medium on which a wobbling track groove is discontinued locally so that an address-dedicated area is provided for the discontinued part. Pre-pits, representing address information recorded, are formed on the address-dedicated area on the track groove. This optical disk has a structure in which the address-dedicated area and a data-dedicated area (for writing information thereon) coexist on the same track groove.
Japanese Laid-Open Publication No. 5-189934 discloses an optical disk on which address information is recorded by changing the wobble frequency of a track groove. In an optical disk like this, an area on which the address information is recorded and an area on which data will be written are not separated from each other along the track.
Japanese Laid-Open Publication No. 9-326138 discloses an optical disk on which pre-pits are formed between adjacent parts of a track groove. These pre-pits represent the address information recorded.
These various types of optical disks have the following problems to be solved for the purpose of further increasing the recording density.
First, as for the optical disk on which address information is recorded as pre-bits within the address-dedicated area on the track, a so-called xe2x80x9coverheadxe2x80x9d occurs to secure the address-dedicated area, and the data area should be reduced for that purpose. As a result, the storage capacity available for the user has to be reduced.
Next, as for the optical disk for recording an address thereon by modulating the wobble frequency of the track, a write clock signal cannot be generated precisely enough. Originally, the wobble of the track groove is created mainly to generate a clock signal for establishing synchronization required for read and write operations. Where the wobble frequency is unique, a clock signal can be generated highly precisely by getting a read signal, having amplitude changing with the wobble, synchronized and multiplied by a PLL, for example. However, if the wobble frequency is not unique but has multiple frequency components, then the frequency band that the PLL can follow up should be lowered (as compared to the situation where the wobble has a unique frequency) to avoid pseudo locking of the PLL. In that case, the PLL cannot sufficiently follow up the jitter of a disk motor or a jitter resulting from the eccentricity of a disk. Thus, some jitter might remain in the resultant recording signal.
On the other hand, where the recording film formed on the optical disk is a phase-change film, for example, a signal read out from such a recording film may have a decreased SNR if data is overwritten on the film repeatedly. If the wobble frequency is unique, the noise components are removable using a bandpass filter having a narrow band. However, if the wobble frequency has been modulated, the filter should have its bandwidth broadened. As a result, the noise components are much more likely contained and the jitter might be further worsened. It is expected that the recording density will be further increased from now on. However, the higher the recording density, the narrower the allowable jitter margin will become. Accordingly, it will be more and more necessary to minimize the increase of jitter by avoiding the modulation of the wobble frequency.
In the structure in which the pre-pits representing the address information recorded are formed between adjacent parts of the groove, it is difficult to form long enough pre-pits in sufficiently large numbers. Accordingly, as the recording density is increased, detection errors might increase its number. This is because if large pre-pits are formed between adjacent parts of the groove, then those pits will affect adjacent parts of the track.
In order to overcome the problems described above, a main object of the present invention is to provide an optical disk medium that contributes to minimizing the overhead and generating a clock signal precisely enough in accordance with the wobble of the track groove.
Another object of this invention is to provide a method and apparatus for reading an address that has been recorded on the optical disk medium.
An optical disk medium according to the present invention includes a track groove thereon. On the optical disk medium, information is recorded along the track groove on a block unit basis. The block unit has a predetermined length. The block unit includes a number of sub-blocks that are arranged along the groove. A sub-block mark is provided within each said sub-block and used to identify the sub-block.
In one preferred embodiment of the present invention, the track groove is preferably provided with a periodic wobble, and the sub-block mark is preferably formed by locally changing the phase of the wobble.
In another preferred embodiment of the present invention, the track groove is preferably provided with a periodic wobble, and the sub-block mark is preferably provided with a wobble having a frequency different from that of the other parts of the track groove.
In still another preferred embodiment, the wobble of the track groove preferably has a shape that represents address information of the block unit.
In this particular preferred embodiment, the wobble of the track groove preferably has a sawtooth shape that represents the address information of the block unit.
Alternatively or additionally, the information represented by the wobble shape of the track groove is preferably also represented by the sub-block.
The present invention provides a method for reading address information from the optical disk medium of the present invention. The method includes the step of generating a first sync signal and multiplying the first sync signal and a read signal together to obtain a first product. The read signal has been detected in accordance with the wobble of the track groove and has a basic frequency. The first sync signal is synchronized with the read signal and has a frequency that is equal to the basic frequency of the read signal. The method further includes the step of generating a second sync signal and multiplying the second sync signal and the read signal together to obtain a second product. The second sync signal is synchronized with the read signal and has a frequency that is twice as high as the basic frequency of the read signal. The method further includes the steps of: integrating the first and second products to obtain an integral; and comparing the integral with a predetermined threshold value, thereby defining the address information.
The present invention further provides an apparatus for reading address information from the optical disk medium of the present invention. The apparatus includes first multiplier, second multiplier, integrating means and comparing means. The first multiplier multiplies a first sync signal and a read signal together. The read signal has been detected in accordance with the wobble of the track groove and has a basic frequency. The first sync signal is synchronized with the read signal and has a frequency that is equal to the basic frequency of the read signal. The second multiplier multiplies a second sync signal and the read signal together. The second sync signal is synchronized with the read signal and has a frequency that is twice as high as the basic frequency of the read signal. The integrating means integrates outputs of the first and second multipliers. And the comparing means compares an output value of the integrating means with a predetermined threshold value, thereby defining the address information.
Another optical disk medium according to the present invention includes a track groove thereon. On the optical disk medium, information is recorded along the track groove. The track groove includes a number of unit sections that are arranged along the track groove and that have side faces displaced periodically along the track groove. Subdivided information is allocated to each said unit section and is represented by a shape that has been given to the side faces of the unit section. Each said unit section has a first side displacement pattern that has been so defined as to make a signal waveform rise relatively steeply and fall relatively gently, or a second side displacement pattern that has been so defined as to make a signal waveform rise relatively gently and fall relatively steeply. An identification mark is formed at the beginning of each said unit section and used to identify the unit section. The identification mark has a side displacement pattern, which is distinguishable from the first and second side displacement patterns, and represents the same information as the subdivided information that is represented by the shape given to its associated unit section.
In one preferred embodiment of the present invention, the information is preferably recorded on the optical disk medium on a block basis. The block preferably has a predetermined length. The block preferably includes a number N of unit sections that are arranged along the track groove.
In another preferred embodiment, the side faces of the track groove are preferably displaced either toward an inner periphery or an outer periphery of the optical disk medium with respect to a centerline of the track groove.
In this particular preferred embodiment, a portion of the side faces, which is shared by at least two of the unit sections, preferably has a constant displacement period within at least one of the blocks.
In still another preferred embodiment, one-bit subdivided information is preferably allocated to each said unit section, and a group of subdivided information representing N bits is preferably recorded on the N unit sections that are included in each said block.
Specifically, each said N-bit subdivided information group preferably includes address information of its associated block to which the N unit sections, where the subdivided information group is recorded, belong.
The prevent invention further provides another method for reading address information from the optical disk medium of the present invention. The method includes the steps of: detecting the identification mark that is provided for each of the unit sections and generating a first signal that corresponds to the information represented by the identification mark detected; generating a second signal that corresponds to the subdivided information represented by the unit section following the identification mark; and defining the subdivided information represented by the unit section in accordance with the first and second signals.
The present invention further provides another apparatus for reading address information from the optical disk medium of the present invention. The apparatus includes: means for detecting the identification mark that is provided for each of the unit sections and generating a first signal that corresponds to the information represented by the identification mark detected; means for generating a second signal that corresponds to the subdivided information represented by the unit section following the identification mark; and means for defining the subdivided information represented by the unit section in accordance with the first and second signals.
Other features, elements, processes, steps, characteristics and advantages of the present invention will become more apparent from the following detailed description of preferred embodiments of the present invention with reference to the attached drawings.